The present invention relates to a fuel reforming apparatus and an electric power generating system having the fuel reforming apparatus, and more particularly to a fuel reforming apparatus of the direct heat exchange type which is suitable for a gas turbine electric power generating system and a electric power generating system having the fuel reforming apparatus.
A fuel reforming apparatus of the indirect heat exchange type, a fuel reforming apparatus of the direct heat exchange type and the like are known types of fuel reforming apparatuses for reforming a raw fuel, such as hydrocarbon, into a hydrogen enriched gas.
For example, the fuel reforming apparatus of the indirect heat exchange type comprises a reactor pipe having a reforming catalyst therein and a burner for applying heat to the reactor pipe, in which a raw fuel which flows into the reactor pipe through one end of the reactor pipe is reformed into a hydrogen enriched gas using the reforming catalyst inside of the reactor pipe, while the reactor pipe is being heated with the burned gas from the burner.
On the other hand, the fuel reforming apparatus of the direct heat exchange type comprises a fuel flow passage having a reforming catalyst inside, in which a part of a raw fuel is partially oxidized (burned) with air inside the flow passage, and the obtained high temperature gas to be reformed is reformed into a hydrogen enriched gas using a reforming catalyst bed. The fuel reforming apparatus of the direct heat exchange type is used in the chemical industry.
Gas turbine electric power generating systems having a fuel reforming apparatus are disclosed in, for example, Japanese Patent Application Laid-Open No. 2-286835 (1990), Japanese Patent Application Laid-Open No. 5-332166 (1993), Japanese Patent Application Laid-Open No. 5-332167 (1993).
Since a fuel reforming apparatus of the indirect heat exchange type described above has a burner for heating the reactor pipe, the size of the apparatus is rather large. Further, if the exhaust gas of the turbine is used for the heat source, it is difficult to obtain the reforming temperature of approximately 700.degree. C. required for the reforming reaction. In other words, taking efficiency into consideration, the exhaust gas temperature of the gas turbine is generally set to nearly 600.degree. C. in the highest case and around 500.degree. C. in a common case. Therefore, it is difficult to obtain the reforming temperature of approximately 700.degree. C. required for the reforming reaction.
On the other hand, the fuel reforming apparatus of the direct heat exchange type is small in size, since a part of the raw fuel is partially oxidized (burned) and the sufficiently high reforming temperature required for the reforming reaction can be obtained. Therefore, the fuel reforming apparatus of the direct heat exchange type is better than the fuel reforming apparatus of the indirect heat exchange type.
The inventors have tried to apply the fuel reforming apparatus of the direct heat exchange type to a gas turbine electric power generating system, but the following problem was revealed. That is, in the fuel reforming apparatus of the direct heat exchange type, the fuel flow passage in which the partial oxidization (burning) occurs is formed of firebricks, and the heat load fluctuation applied to the firebricks is small in a fuel reforming apparatus in the chemical industry, where it is used for a long period of time under a constant operating condition. Therefore, cracks hardly occur in the firebricks under such constant load conditions. On the other hand, the heat load fluctuation applied to the firebricks is large in a gas turbine electric power generating system, and so cracks are apt to occur in the firebricks with such load fluctuation. Therefore, if the conventional fuel reforming apparatus of the direct heat exchange type is directly applied to a gas turbine electric power generating system, there is a possibility that cracks in the firebricks will result. In addition to this, there is a possibility that a secondary failure due to fracture of the broken firebrick will occur. The disclosed gas turbine electric power generating system described above therefore employs a fuel reforming apparatus of the indirect heat exchange type.